Lighting system



June 25, 1957 CQL. scio'r'r El AL LIGHTING SYSTEM Filed Nov. 16, 1955 nitecl States Patent 2,797,367 Patented June 25, 1957 ice LHGHTING SYSTEM Charles I... flcott, Parma, and Thomas N. Humphreville,

Lorain, @hio, assignors to Westinghouse Electric Qorporation, East Pititsburgh, Pin, a corporation of Pennsylvania Application November 16, 1955, Serial No. 547,142

11 Claims. ((31. 315-162) This invention relates to an airport approach lighting system, and more particularly to a system for flashing a series of light units in a predetermined sequence to light the approach path to a runway.

There is shown in a previously filed patent application entitled Approach Light System by W. A. Pennow, issued on February 7, 1956, as Patent No. 2,734,180, and assigned to the same assignee as this application, a lighting system for lighting the approach path to an airport runway. The system shown in the Pennow patent consists of a series of brilliant lights of the krypton type, which are flashed in sequence to simulate a streak of lightning which indicates the direction of the airport runway. In order to flash the lights disclosed in the Pennow patent there .is disclosed a mechanically driven controller utilizing a plurality of switches which are sequentially closed to flash the various lamps in sequence. This type of mechanically driven controller while adequate for the purpose has some disadvantages, such as the limited life of the switches and the ditficulty of maintaining mechanical adjustment to give uniform flashing of the various lights. It also requires considerable wiring since a separate set of leads must be run from each light to the controller in order that the lights may be controlled by the controller. Since the lighting system extends for about a half mile from the end of the runway this requires a large amount of wire.

This invention provides such a lighting system in which each light unit has means for receiving a signal from the preceding unit and utilizing the signal to flash its light, and then transmitting the signal to the next light unit in line after storing it for a predetermined time. The signal from the last unit is returned to the first unit to commcnce a new sequence, and means are provided for supplying a new signal to the first unit if the signal of the last unit fails to return. While various :Ineans could be used to perform the above operations, suchas relays or vacuum tube oscillators, the preferred embodiment of the invention-employs vacuum tube oscillators andiisidescribed later. In this embodiment of the invention a signal from a multivibrator in one light unit is used to trigger a multivibrator in the next light unit which, in turn, triggers multivibrators in succeeding light units until the complete series of light units has been flashed. The signal from the last multivibrator is returned to a free running oscillator at the beginning of the series of lights to again trigger the first multivibrator to begin a new sequence. Also preferably included in each multivibrator unit is a bypass circuit to 'bypass the incoming signal in case that particular multivibrator is malfunctioning so that the remainder of the lights maystill be flashed and a signal returned to the free running oscillator. In case the signal from the last'multivibrator does not return to the free running oscillator to commence a new sequence, the free running oscillator will againtrigger the first multivibrator. Of course,'the free running oscillator should have a frequency lower than the frequency for flashing the complete seriesof lights. "-Byineluding variable time delay means in the individual multivibrator circuits the delay between the flashing of successive lamps can be accurately controlled to eliminate the difliculty of maintaining the mechanical adjustments required of the system disclosed in the Pennow patent.

Less wire will be required to connect a system constructed in accordance with this invention, since only a single lead is required between adjacent light units with a lead running from the last unit to the first unit. This is a considerable reduction in wiring over the arrange ment disclosed in the Pennow application, which required a separate lead from the controller to each light unit. The system disclosed in this application also has the advantage in that its components have a longer service life and require less maintenance than components of the mechanical system in the .Pennow patent which, in turn, means that the disclosed system will have greater .dependability.

Accordingly, the principal object of this invention is to provide a novel approach lighting system consisting of a series of-light units each of which has means for receiving a signal, and means for utilizing the signal to flash its light and then transmitting the signal to the next unit after storing it for a predetermined time, with the signal from the last unit being returned to the first unit.

Another object of this invention is to provide a novel approach lighting system consisting of a series of light units, each of which has means for receiving a signal and means for utilizing the signal to flash its light and then transmitting the signal to the next unit after storing it for a predetermined time, with the initial signal being supplied by a timing device and the signal from the last unit being returned to the timing device prior to its supplying a new signal.

Another object of this invention is to provide a novel approach lighting system consisting of a series of light units, each of which has means for receiving a signal and means for utilizing the signal to flash its light and then transmitting the signal to the next unit after storing it for a predetermined time, with the initial signal being supplied by a timing device and the signal from the last unit being returned to the timing device prior to its supplying a new signal, and in addition, each unit having a bypass means to bypass the signal in case of failure of its receiving, transmitting or storing means.

Another object of this invention is to provide a novel means for flashing a series of light units in a predetermined time sequence by the use of a single shot multivibrator associated with each light unit.

Another object of this invention is to provide a novel means for flashing a series of lights including ;a single shot multivibrator associated with each light and a control oscillator for supplying the initial signal of a lower frequency of oscillation than the time required for flashing the entire series of lights and returning -a signal to the control oscillator.

Another object of this invention is to provide a novel means for flashing a series-of lights by means of a'single shot multivibrator associated with each light and having a variable delay circuit for storing the pulse received from the preceding light unit before it is transmitted 'to the succeeding light unit and a bypass circuit to'bypass the pulse if a particular multivibrator is malfunctioning.

These and other objects of this invention will-be more readily understood by those skilled in the art from the following detailed description of a preferred embodiment shot multivibrators for triggering the lights shown in Fig. 1 and the free-running oscillator for supplying the initial triggering pulse.

Shown in Fig. 1 is an approach lighting system in which a plurality of flashing light units 84 are flashed in a predetermined sequence to simulate a streak of lightning indicating the direction to the end of the runway 11. The lights extend out from the end of the runway in the approach path to the runway, and are spaced apart so that when they are flashed in sequence from the outer end of the line of lights toward the runway 11, with a set time delay period between the flashing of adjacent lights, they will simulate a streak of lightning traveling toward the runway .11. Each of the light units 84 has means for receiving a signal, utilizing the signal to flash its associated light 82, then storing the signal for a predetermined time before transmitting the signal to the next light unit 84. The last light unit 84 in the system adjacent the end of runway 11 returns the signal by means of a lead 86 to the control oscillator which may be incorporated within the first unit, which is. the most remote unit from the end of runway 11, to normally commence a new flashing sequence. The control or free running oscillator is preferably mounted in the first light unit 84 to supply the initial signal to commence a flashing sequence. While the free running oscillator could be used to directly initiate flashing of the line of lights, in accordance with this invention, it has a lower frequency of oscillation than the time required for flashing the complete series of lights. Thus the signal can return from the last light unit and start a new sequence before the free running oscillator supplies another signal. In this way a succeeding cycle of flashing the entire row of lights cannot occur until the preceding cycle terminates. The signal from the last unit can thus be used to trip the free running oscillator and start it on a new oscillation thus eliminating the possibility of two signals separated by a short time interval being received by the first unit 84. In case the signal from the last unit 84 does not return to trip the free running oscillator, it will continue its oscillation and supply a signal to the first unit to commence a new flashing sequence. Also included in each light unit is a means for varying the time during which the signal-is stored before it is transmitted to the next unit. Thus the delay period of each unit can be accurately adjusted so that it is the same as the delay period for the remaining units.

Shown in Fig. 2 at the left-hand side is the free running unbalanced oscillator, the output of which is connected to the variable time delay single shot multivibrator of the first unit 84, Whose output in turn is connected to a second variable time delay single shot multivibrator enclosed in the second light unit 84, and so on. As previously mentioned, the output of the multivibrator of the last unit 84 is returned to the free running oscillator by conductor 86 to again trigger the first multivibrator to commence a new sequence.

The free running oscillator consists of two vacuum tube discharge devices and 12, which are shown as triodes having plates 14 and 16, control grids 18 and 20, and cathodes 22 and 24, respectively. The plate 14 of the tube 10 is connected to a direct current source of positive potential B+ through a resistance 26, and the plate 16 of the tube 12 is also connected to a direct current source of positive potential through a resistance 28, which may be the same source B+. The cathode 22 of the tube 10 and the cathode 24 of the tube 12 are connected to ground, which in turn is connected to the negative terminal B of the direct current source. The plate 16 of the tube 12 is connected to the control grid 18 of the tube 10 through a coupling capacitor 38. The control grid 18 in turn is connected to ground through a grid leak resistor 40. The plate 14 of tube 10 is connected to the control grid 20 of tube 12 through a coupling capacitor 34. The control grid 20, in turn, is connected to ground through a grid leak resistor 36. The control grid 18 of tube 10 is also connected to the conductor 36 to receive an incoming pulse through .a coupling capacitor 30, which, in turn, is connected to ground through a resistance 32.

In order to operate the free running oscillator, the direct current source may be obtained from any well known power supply, such as a full wave rectifier vacuum tube power supply under the control of a suitable switch.

When the oscillator is energized, as is well known, one of the tubes, for example the tube 10, will become conducting first. Due to the voltage drop across resistor 26 this will lower the voltage applied to capacitor 34 permitting it to discharge which will cause the grid 20 to be negative and prevent tube 12 from conducting. However, after capacitor 34 discharges the voltage on grid 29 will rise to a positive value such as to permit tube 12 to conduct. In the meantime, capacitor 38 has become charged at a relatively high potential and as tube 1?. begins to conduct the potential applied to capacitor 38 drops, permitting it to discharge and lower the potential on grid 13 to cut off conduction of tube 10. The re erse operation then takes place which again renders tube 10 conducting, cutting off tube 12, and so on. When the tube 12 starts conducting and tube 10 cuts off, the voltage drop through the resistor 26 will be eliminated thus raising the positive potential applied to the plate 14 and at the same time sending a positive pulse through the lead 27 to trigger the first multivibrator.

The time constant of capacitor 38 and resistance 40 should be very large in comparison to the time constant of capacitor 34 and resistance 36 so that the tube 10 remains cut off for the major part of the cycle of the oscillator. This will allow the complete series of lights to be flashed and a positive pulse returned from the last light unit by conductor 86 to trigger tube 10 before capacitor 38 completely discharges. In case the positive pulse from the last light does not return the capacitor 38 will completely discharge, and the potential on grid 18 of tube 10 will ultimately rise as previously explained. Tube 10 will then conduct since capacitor 34 is charged and capacitor 34 will discharge through tube 10 and apply a negative potential to grid 20 of tube 12 which will then cut off. Tube 10 will then cut off as explained above, thus sending another positive pulse to trigger the first multivibrator.

The variable delay single shot multivibrators in the light units each comprise two vacuum discharge tubes 52 and 54. As shown in Fig. 2, the tubes 52 and 54 are triodes having plates 56 and 58, control grids 60 and 62, and cathodes 64 and 66, respectively. The control grid 60 of tube 52 is connected, when contacts 90 of relay 88 are closed, to the plate 14 of tube 10 through a capacitor 50. The control grid 60 is also connected to ground through a grid leak resistor 78. The plate 14 of the tube 10 is also connected to the primary coil of a transformer which is used for increasing the voltage of the pulse from tube 10 to a value suflicient to flash a low pressure vapor lamp 82. An example of a suitable low pressure vapor lamp 82 is a krypton lamp such as that disclosed in the above-mentioned Pennow patent. The lamp 82 may be designed so that when a voltage of approximately 2000 volts is applied to its electrodes 81 and 83 from anysuitable source, such as power supply 35, which may be similar to that shown in Fig. 8 of the Pennow patent, an additional pulse from the transformer 80 when applied to a third electrode 85 will ionize the gas within the lamp and cause the lamp to flash.

The plate 56 of the tube 52 is connected to a suitable direct current source of positive potential B-lthrough a resistor 68, and the plate 58 of the tube 54 is also connected to the source of direct current positive potential B+ through a similar resistor 70. The cathode 64 of the tube 52 and the cathode 66 of tube 54 are connected to ground through a common resistance 72. The plate 56 of the tube 52 is connected to the control electrode 62 of the tube 54 through a coupling capacitor 76. The conttfol electrode 62 is also connected to the cathodes 64 and 66 through a variable resistance 74. A suitable adjustable tap 87 is provided on the resistance 68 which connects the .plate 56 of the tube 52 to the source of positive potential for taking olf a pulse for triggering the succeeding multivibrator to lire its succeeding lamp 82. CapacitorSO allows the pulse to pass to the next unit while blocking the source current. The complete multivibrator unit is enclosed with its associated lamp 82 within a suitable lamp housing 130 represented by the dotted lines of Fig. 2 to form a light unit 84. The lamp housing 130 could be of any desirable shape, such as the lamp housing 12 shown in Fig. 4 of the Pennow patent.

The inultivibrator unit could be enclosed in a separate container, similar to the power supply 35 in Fig. 4 of the Pennow patent, and mounted in the housing 130.

A means is provided in each multivibrator unit for bypassing the unit if it has failed, thus allowing the remaining lights in the circuit to flash. This includes a relay 88 having contacts 90 operable to connect the incoming :pulse to the control grid 60 of tube 52, and contacts 92 for connecting the incoming .pulse to the lead going to the next unit, so that the positive pulse may bypass the multivibrator unit. When an incoming positive pulse is received it will energize second relay 94 through-a rectifier, such as diode 96, and a gap, such as a neon lamp 98, with the diode 96 connected so as to pass only a positive pulse to relay 94. A capacitor 100 is connected in parallel with the coil of relay 94 in order to delay the opening of the relay until another positive pulse is received, the period between positive pulses being on the order of one-half second. The contacts 102 and 104 of relay '94 connect the coil of relay 88 to ground to energize relay 88 or disconnect the coil from ground to deenergize relay 8%, depending on the position of relay 106. Relay 106 is connected to the plate 58 of tube 54 through a rectifier, such as diode 108, and a gap, such as neon lamp 110, with diode 108 connected so as to pass only a negative current to relay 106. A capacitor 112 is connected in parallel with the coil of relay 106 to delay the opening of the relay so that it remains closed while tube 52 conducts. The contacts 114 and 116 of relay '106 connect the coil of relay 88 to ground or disconnect the coil from ground depending on the position of relay 94 as will be explained below. A capacitor 110 is connected between the diode 108 and the plate 58 of tube 54 'to block the 13-}- power supply from relay 106 and to supply a source of potential to energize relay 106 when it discharges.

In order to operate the series of connected multivibrators, the previously described source "of direct current B+ potential is connected to the plates 56 and 58 of tubes 52 and 54, respectively, and to relays 88. Each relay 88 will be energized because both relays 94 and 106 are deenergized; thus closing their contacts 104 and 114, and assume its normal position closing its contacts 90 so that the positive pulse will be received by tube 52. Capacitor 76 will commence to charge and cause tube 54 to conduct, and tube 54 will commence to conduct until grid 60 of tube 52 receives a positive pulse from the free running oscillator. When contacts 90 of relay 88 close, the positive pulse from the free running oscillator will be applied to the control grid 60 of tube 52. The positive pulse will also flash the low pressure vapor lamp 82 by means of the step-up transformer 80 and power supply 3'5. When the positive pulse is applied to the control grid 60 of tube 52 it will cause the tube 52 to conduct and charge capacitor 118. The tube 52 will conduct until the capacitor 76 .is iully discharged which will completely cut off tube -4. Tube 54 will again start to conduct as capacitor .76 starts to charge, thus increasing the positive voltage on cathode 64 of tube 52. This action will continue .until tube 52 is cut ofi and tube 54 is fully conductive. When tube 52 cuts 01f a large positive potential willappear at. tap 87 on resistor 68 7 'due to the decreased voltage drop across resistor 68.

This positive pulse will be transmitted to the nextsingle shot multiv-ibrator to trigger its tube 52 and flash "the next-lamp 82.

The positive pulse received by the first multivibrator will also energize relay -94 of the bypass circuit closing its contacts 102 and opening its contacts 104 and charge capacitor 100. When the contacts 104 open the relay 88 will momentarily be deenergized, thus closing its contacts 92. In the meantime the multivibrator has operated and tube 54 has again become conducting thus allowing condenser 118 to discharge sending current in a reverse direction through diode108 and neon lamp 110 to operate relay 106 closing its contacts 116 and opening its contacts 114. When contacts 116 close, relay 88 will be reenergized through closed contacts 102 of relay 94 again closing its contacts 90 and opening its contacts 92. When contacts 90 of relay 88 close, the unit will be ready to receive the next positive pulse from the free running oscillator. Of course, capacitors and 1-12 and relays '94 and 106 should be substantially identical and have suitable electrical characteristics so that the relays remain closed for more than the period between positive pulses received by the multivibrator. The neon lamps 98 and isolate the capacitor relay network so that the capacitors discharge only through their respective relays 94 and 106 instead of through the multivibrator, thus delaying their opening until another positive pulse is received instead of discharging through the multivibrator circuit.

in operation, if the 13+ power supply should fail, relay 83 will be deenergized and its contacts 92 will close thus passing the unit. If the multivibrator unitfails to function,

tube 54 will not become conducting; thus relay 106 will not be energized and relay 88 will remain deenergized by the action of relay 94 when another positive [pulse is received. This positive pulse will maintain relay 94 energized thus closing its contacts 102 and opening its contacts 104 which will 'deener'gize relay 88 since it will not be connected to ground a's'long as relay 106 remains deenergized keeping its contacts 116 open. This in turn, will allow the positive pulse to bypass the unit through the closed contact 92 of relay 88. If the incoming positive .pulse is not received from the previous unit, relay 94 Will deenergize after the time delay of capacitor 100 and its contacts 104 will close and relay 8% will be 'deene'rgized because relay 106 will remain energized for a longerperiod because capacitors 100 and 112 are identical and capacitor 112 discharges after capacitor 100. Thus, if a previous unit has failed and has not had time to bypass, all of the following multivibrator units will bypass until the next positive pulse recycles the first bypassed multivibrator unit. The 'next positive pulse will reenergize relay 94 and start 'a new cycle of operation as described above. Thus, the main function of the circuit composed of diode 96, neon lamp 98, relay 94 and-capacitor 100 is to reset the bypass circuit for the receiving of another positive pulse in the event that a previous unit in the system fails and interrupts the positive pulse longer than the delay time of relay 94 due to the discharge of capacitor 100.

Each multivibrator will continue with tube 54 conducting until another positive pulse is received and tube 52 again conducts. The length of time that tube 52 of each multivibrator conducts, and thus the time delay between the receiving of a'positive pulse and its transmission to the next single shot multivibrator can be accurately controlled by changing the time constant oftlie capacitor 76 and resistor 74. This can be done by adjusting the variable resistor 74. Thus, the time delay between the flashing of succeeding lights can be accurately set and controlled.

The positive pulse transmitted from the first multivibrator to the second multivib'ra'tor will flash the lamp 82 associated with "the second 'multivibrator and cause its tube 52 to conduct. The second multivibrator will operate in eiractly the same manner as described above for the first multivibrator. When the tube 54 of the second multivibrator starts to conduct, a positive pulse will appear at the tap 87 of its resistance 68 which will be transmitted through its capacitor 50 by means of a lead to the next light unit. The last light unit will transmit its pulse by means of the lead 86 back to the control grid 18 of the tube 10 of the free running oscillator and it will arrive at the tube 10 before the tube 10 would normally become conducting. Of course, the total of the time delays of the individual units must be adjusted so that it is less than the frequency of the free running oscillator. The positive pulse when applied to the control grid 18 will cause the tube 10 to conduct thus cutting off tube 12. Tube 10 will conduct until the capacitor 34 completely discharges after which tube .12 will start to conduct thus cutting off tube 10 and supplying a new positive pulse to the first single shot multivibrator. The period for flashing all lamps and returning the positive pulse to the oscillator is on the order of one-half second, thus the oscillator frequency should be larger than this value. This positive pulse will trigger the first multivibrator and start a new sequence of flashing of the series of lamps. The frequency of oscillation of the free running oscillator can be controlled by changing the values of the capacitors 34 and 38 and the resistances 36 and 40 so that its frequency is lower than the time required to flash the complete string of lamps as explained above.

While but one embodiment of this invention has been described with specific reference to the flashing of a plurality of lights used in an approached lighting system for an airport runway, it will be apparent to those skilled in the art that it can be adapted to flash any series of lights.

We claim as our invention:

1. An electrical system to control the flashing of a plurality of series connected light units in a predetermined timed sequence comprising, a vacuum tube oscillator connected to the first unit, a vacuum tube multivibrator associated with each of said light units, the multivibrator of the first unit having means for receiving a pulse from said oscillator to flash its associated light, said multivibrator in addition having transmitting means for supplying a pulse to the multivibrator of the second unit, each additional multivibrator receiving a pulse from the preceding multivibrator and the last multivibrator being connected to said oscillator to supply a pulse to trigger said control oscillator at a frequency above its control frequency.

2. An electrical system to control the flashing of a plurality of series connected light units in a predetermined timed sequence comprising, an unbalanced oscillator connected to the first unit, a single shot multivibrator associated with each of said light units, the multivibrator of the first unit having means for receiving a pulse from said oscillator to flash its associated light, said multivibrator in addition having transmitting means for supplying a pulse to the multivibrator of the second unit, each additional multivibrator receiving a pulse from the preceding multivibrator and the last multivibrator being connected to said unbalanced oscillator to supply a pulse to said unbalanced oscillator at a frequency above its control frequency.

3. A light unit comprising, an incoming conductor for transmitting an electrical pulse to the light unit, means mounted in said light unit for supporting a gas discharge light, amplifying means associated with said light unit for amplifying said electrical pulse when received to a magni tude sufficient to flash such a light, storing means also associated with said unit operating in response to the receiving of said pulse for storing said pulse for a predetermined period, an outgoing conductor for thereafter transmitting said pulse to another light unit, and a bypass means connected to said incoming and outgoing conductors and operating in response to the failure of said storing means for bypassing said unit.

4. A light unit comprising, an incoming conductor for transmitting an electrical pulse to the light unit, means mounted in said light unit for supporting a gas discharge light, amplifying means associated with said light unit for amplifying said electrical pulse when received to a magnitude sufiicient to flash such a light, storing means also associated with said unit operating in response to the receiving of said pulse for storing said pulse for a predetermined period, an outgoing conductor for thereafter transmitting said pulse to another light unit, means connected to said storing means for varying the period said pulse is stored, and a bypass means connected to said incoming and outgoing conductors and operating in response to the failure of said storing means for bypassing said unit.

5. A light unit comprising, an incoming conductor for transmitting an electrical pulse to the light unit, means mounted in said light unit for supporting a gas discharge light, amplifying means associated with said light unit for amplifying said electrical pulse when received to a magnitude sufficient to flash such a light, storing means also associated with said unit operating in response to the receiving of said pulse for storing said pulse for a predetermined period, an outgoing conductor for thereafter transmitting said pulse to another light unit, and bypass means comprising, a first switching means for connecting said incoming conductor to said storing means or to said outgoing conductor, a second switching means operating in response to the receiving of said electrical pulse to actuate said first switching means to connect said incoming conductor to said outgoing conductor, and a third switching means operated by said storing means for actuating said first switching means to reconnect said incoming conductor to said storing means.

6. A variable time delay single shot multivibrator for flashing a low pressure vapor lamp comprising, two vacuum tubes, each including at least a plate, a cathode and a control grid, the cathodes of said tubes being connected to ground through a common resistor, the plates of said tubes being connected to a source of positive potential through separate resistors, means including a variable resistance for connecting the control grid of one of said tubes to both of said cathodes, means including a fixed resistance for connecting the control grid of the other of said tubes to ground, means including a capacitor for connecting the plate of said other tube to the control grid of said one tube, means including a capacitor for connecting a signal source to the control grid of said other tube, additional means for increasing said signal source to the magnitude required to flash a low pressure vapor lamp, and output means for transmitting a signal from said one tube to another connected multivibrator.

7. A light unit comprising an incoming conductor for transmitting a pulse to the light unit, means mounted in said unit for supporting a gas discharge light, means associated with said light unit for amplifying an electrical pulse received by said unit to a magnitude sufi'icient to flash such a gas discharge light, storing means also in said unit operating in response to receiving of said pulse for storing said pulse for a predetermined period, an outgoing conductor for thereafter transmitting said pulse to another light unit, and additional means connected to said storing means for varying the period said pulse is stored.

8. An approach lighting system comprising a plurality of series connected light units flashed in a predetermined sequence, the last unit being connected to a timing device, said timing device being connected to the first unit, each unit comprising a light with means for receiving a signal, means for utilizing said signal to flash a gas dis charge light and means operating in response to receiving of said signal for storing said signal for a predetermined time before transmitting said signal to the succeeding light unit, the signal from the last light unit being transmitted to said timing device, the signal from the last unit triggering said timing device to commence a new sequence of flashing said light units.

9. An approach lighting system comprising a plurality of series connected light units flashed in a predetermined sequence, the last unit being connected to a timing device, said timing device being connected to the first unit, each unit comprising a light With means for receiving a signal and utilizing said signal to flash said light, storing means operating in response to the receiving of said signal for storing said signal for a predetermined time before transmitting said signal to the succeeding light unit, the signal from the last light unit being transmitted to said timing device, the signal from said last unit triggering said timing device to start a new sequence of flashing the light units, and additional adjustable means connected to said storing means for varying said storing time so that the light units when flashed will simulate a streak of lightning.

10. An electrical system to control the flashing of a plurality of series connected low pressure vapor light units in a predetermined timed sequence comprising, a control oscillator, a vacuum tube multivibrator associated with each of said light units, each of said multivibrators in addition having means for receiving a pulse and increasing said pulse to the magnitude required to flash the light associated with said unit, each of said multivibrators in addition having bypass means for bypassing said pulse in response to failure of said multivibrator, the multibrator of the first unit having means for receiving a pulse from said oscillator to flash the first light, said first multivibrator in addition having means to transmit a pulse to the multivibrator of the second unit, the multivibrator of each additional unit receiving apulse from the multivibrator of the preceding unit and the multivibrator of the last unit having means to transmit a pulse to said control oscillator at a frequency above its control frequency to commence a new sequence.

11. A bypass device for bypassing one of a series of connected multivibrator units comprising, a first switching means for connecting an incoming conductor to the control grid of a first vacuum tube or to a lead that bypasses said multivibrator, a second switching means operating in response to the receiving of an incoming pulse to actuate said first switching means to bypass said multivibrator, a third switching means operating in response to a second vacuum tube of said multivibrator to actuate said first switching means to reconnect said incoming conductor with the control grid of said first tube before the receiving of another incoming pulse by said multivibrator unit.

No references cited. 

